1. Field of the Invention
This present invention is directed to systems and methods for fluid transfer in subsea operations; to heave compensation in subsea operations; to systems and methods for compensating for the movement of sea-going vessels used in wellbore subsea operations; and, in certain particular aspects, to a heave compensation system located subsea.
2. Description of Related Art
In many situations, interventions are required to maintain the performance of an oil or gas well. Interventions typically include but are not limited to: removing debris from a well, shifting production levels in a well, unloading fluid from a well, stimulation of a production zone, and well logging. Often interventions require injection of one or more fluids into a well; e.g. but are not limited to: water, nitrogen, hydrate inhibitors, acids, and cements. Such fluids are transported to the well site, stored in transportable containers, and then pumped into well with specialized pumping equipment.
Well interventions can be performed on subsea wells. However, such interventions can be more complicated due to inaccessibility of the well. A typical subsea well intervention includes utilization of a mobile offshore drilling unit and related specialized equipment. This method of well intervention is costly and time consuming.
Certain prior art methods of performing well subsea interventions use a tool which is deployed from a deployment vessel and attached to the subsea well. The tool, known as a subsea intervention module, includes coiled tubing equipment, intervention tools, well control equipment, control systems, and other equipment required to perform well interventions on subsea wells. The intervention module can be powered and controlled remotely from a deployment vessel via control umbilical.
Intervention fluid and hydrate inhibitor are transferred from the deployment vessel to the tool via an intervention fluid conduit. The intervention fluid conduit is known as the pump down line or “PDL” which consists of a specialized string of steel coiled tubing which is designed to transfer a plurality of discrete fluids simultaneously. The PDL is deployed and connected to intervention module. Surface equipment lowers one end of the PDL to the intervention module on the subsea well after the intervention module has been deployed.
Wave motions at the surface can cause a deployment vessel to heave. Because a PDL is suspended from the deployment vessel, the PDL will heave with the same frequency and as the vessel. The wave-induced PDL motions must be controlled to allow for connection of PDL to an intervention module and to prevent damage to the PDL and any components of the intervention module which could come in contact with the heaving parts.
In the past flexible hoses have been used, but many of the intervention fluids have chemical properties which are incompatible with the lining materials of flexible hoses. High pressure gas intrusion into hose lining can cause separation of the lining from the hose. In addition, pressure differentials between the intervention fluid stream and the sea outside the fluid passages which would cause a collapse of the flexible hose. Also, the constant movement of the flexible hose can cause premature failure of the hoses.
The prior art discloses a wide variety of systems, apparatuses, and methods to compensate for the movement of vessels used in subsea operations. U.S. Pat. Nos. 3,943,868; 3,991,837; 4,858,694; 5,190,107; 4,176,722; 4,059,148; 4,934,870; 4,899,823; 6,343,893; 4,962,817; 6,386,290 and the prior art references cited therein provide a small sampling of the prior art directed to heave compensation and to compensation for the movement of a vessel.
U.S. Pat. Nos. 6,276,454; 6,053,252; 6,698,520; 6,488,093; 6,659,180; 6,460,621; 6,547,008; 6,763,889; and U.S. application Ser. Nos. 10/368,762 filed Feb. 19, 2003 and 10/204,606 filed Feb. 20, 2001, and the prior art cited in these patents and applications, provide a small sampling of prior art references directed to subsea operations and to subsea intervention.
There has long been a need, recognized by the present inventor, for effective and efficient subsea intervention fluid transfer systems and heave compensation systems.
There has long been a need, recognized by the present inventor, for an efficient and effective heave compensation system for use with relatively small and/or monohull vessels.
There has long been a need, recognized by the present inventor, for an efficient and effective heave compensation system for use with a pumpdown line which is deployed from a fixed system on the deck of a vessel.